Apparatus for manufacturing prestressed concrete members



Oct. 10, 1961 B. c. GERWICK, JR 3,

APEARATUS FOR MANUFACTURING PRESTRESSED CONCRETE MEMBERS Filed Feb. 25, 1957 4 Sheets-Sheet 1 APPARATUS FOR MANUFACTURING PRESTRESSED CONCRETE MEMBERS 4 Sheets-Sheet 2 Filed Feb. 25, 1957 mu mH-l nl INVENTQR. Ben C 6erw/ck,J/:

ATTORNEVI Oct. 10, 1961 B. c. GERWICK, JR 3,003,217

APPARATUS FOR MANUFACTURING PRESTRESSED CONCRETE MEMBERS 4 Sheets-Sheet 3 Filed Feb. 25, 1957 INVENTOR.

6/7 C. Gen/Vick, J/T

Oct. 10, 1961 B. c. GERWICK, JR 3,003,217

APPARATUS FOR MANUFACTURING PRESTRESSED CONCRETE MEMBERS Filed Feb. 25, 1957 4 Sheets-Sheet 4 INVENTOR. 56/7 C Germ/wk, Jr?

ATTORNEYS United States Patent s 003 217 APPARATUS non. MANUFACTURING ransTREssE-n coNcnnrn Marianas Ben C'. Gerwick, .Ir.,;akiand, Califi, assignor'toBen C.

Gerwick, Inn, San Francisco, Calif, a corporationaof California Filed Feb..25, 1955'7, Ser. No. 642,124 4 Claims. (Cl. 25-118).

This inventionrelates generally .to the manufacture-oft.

reinforced;concretebeams, and particularly to. beams provided with pretensioned reinforcing members...

The construction industry has recognized theadvantagesof concreteibeams andlike structural Inembersthat.

are prestressed, The desirability of prestressing by employing deflected. tensioned reinforcement has also been recognized, particularly as applied to relatively long, beams. However many problems have been encountered. TheaposL which have prevented wide commercial use. tensioning method-has. been attempted for this. purpose, buthas notbeen successful, due largelyto itsinherent limitations and lack. of positive control. In certain instances long beamsthaving deflected pretensioned strands have .beenproduced, but the cost has been uneconomical, and the equipment employed has been elaboratev and expensive to. install .and operate. Relatively crude equipment has been proposed, which is provided withfa jack of the. above character which permits considerable.

flexibility andadjustment with respectto the size, shape andtype, of concrete member being made, and 'with respect, to the pattern and extent of deflection of therein? forcing strands.

Additional objects and features of the invention will' appear from the following description in which thepreferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1 isa plane view schematically illustrating apparatus incorporating the present invention.

FIGURE 2 is a side elevational view of the apparatus shown in FIGUREj 1 with three harpingunits beingapplied to deflect the reinforcing strands.

FIGURE 3 is a cross sectional viewon an enlarged scale takenalong the line 33 of FIGURE 1, and show: ing. the construction of one of the harpingunits.

FIGURE 4 isa cross sectional detail .taken along the line.44 of FIGURE 3.

FIGURE 5 is an enlarged detail in section illustrating theattachment between thedeflectingyokes or forks and the pull cable.

FIGURE 6 is a view taken along the line 66 of FIG-, URE 5.

FIGURE 7 is a side elevational view partly in section, illustrating a longer pull rod for making connection with one of thecable engaging forks.

FIGURE 8is a side elevational view similar to. FIG- URE 3 but showing a modified type of harping unit.

FIGURE 9 is a cross sectional view. taken along the line 9-..9 of FIGURE .8.

3.003217, Patented Oct. .10, 1961.

ice

FIGURE ,10 is a cross sectional view taken along ,the line 10-"10 of FIGURES.

The present invention employs rigid means forming ahorizontal workingbed, and which serves to carry oneor. more forms forupouring a beam of the desired fcontour. Horizontally spacedv means are provided for engaging and. positioning reinforcing members at locationscorrespondy inggenerally to the ends of the beam being cast A P1 11 rality of harping units are associated with the bed and; serveto engage andapply force to the reinforcing members wherebythey are deflected downwardly to the desired extentto produce thedesired'curvature. Preferably the reinforcingmembers are engaged in at least three points, whereby the curve obtained approximates a parabola. Each oftheharping units is of special construction as willbe presently described.

Referringto the drawing, the rigid bed It} has a. length somewhat greater than the longest. beam which is to be. manufactured. In some instances this bed may be of such length as to permit casting-a series of beams simul-g taneously. In practicelthe bed may consist of structural steel members 11, having suitable anchorage to the ground. Adjacentthe ends of the bed suitable means are provided for anchoring the reinforcing, members and for applying suitable tension. In FIGURE loneanchoring means isindicated schematically at 12, and can consist/of a rigidmemberthrough which" the ends of, the reinforcingmembers extend, and to-which-they are an: chored. This 'member --in turn is rigidly mountedjupon the bed. At the other end of the bed the reinforcing members extend through the member 13; which-is likewiserigidly anchored to the-bed; Suitable'jacking means 14,- as for example-of the hydraulic'typeis attachedto the ends ofthe strands to-apply the desired tension;

Various typesof molding or casting forms cambe-positioned upon th'e bed, dependingupon-the contour-of theconcrete-member desired. As illustrated in FIGURE 3i the mold can'consist of a bottom horizontal soflit--board* l6'together with theside'walls 17, which-are hinged at 18: End closure plates 21 'cantbe-provided with suitable perforations to receive-the reinforcing-strands. Distribution of the perforations determines the distribution"pat tern of the beam. Near-the ends-of=the formit-is-desir able to provide additional means for supporting the rein-'- forcing members at a desired levelr- This means can be' in the form of :a standard 22 formed to provide verticallyspaced horizontalsupporting rods. Theserods engage and support the cables -atthes desired levels.-

E'ach: of the harping unitsv for engaging the reinforcing: members consists of a device locatedwithin the casting form, together withmeans exterior of the formfor applying: downward deflecting force. Thus. referring particularly to FIGURES 38 each" harping unit consistsof'a yoke-like member 26:having its lowerend attached to the rod-like memberZ'Zz Apertures in the side of theyoke carry the. removable rodslsforaengaging the reinforcing strands. Byturningsthe member 2.7,it can :be disengaged with respect to thenut 29 and thus detached from the yoke. In. the modificationz of FIGURE 7 the: member 27a is of extended; length andzin the form.of?a; polished and tapered rodas illustrated, tocpermit-itsrea moval from .the hardened concrete. The lower end of x member 27 (or 2711) is pivotally connected to a half; sheave or saddle 32 which is engaged by the looped-1; cable 33.

A structural frame 36. extends laterally of the working: bed, and carries thebearings 37 for journalling the roller 38. This roller is provided with grooves 35 adapted too be engaged by the two lengths of the-cable-33. Theendsr; of the cableare attached to a head, 40-,which is slidably guided within-the frame. A rod ,39 is attached-tothe; headand extends from onevend. of thedframe, Where ittisj;

threaded and provided with nut 41. By turning nut 41, it is evident that the rod 39 can be drawn to the left as viewed in FIGURE 3, thus applying pull to the cable 33, and pulling downwardly upon the yoke 26.

In FIGURE 1 three harping units of the type described above have been distributed along the length of the bed. Generally it is desirable to locate one unit with a short rod 27 midway between the ends of the form, together with two or more additional harping units with the large rods 27a for deflecting the reinforcing members at one or more points between the midpoint and the ends of the beam. In some instances a single unit is sufficient.

Operation of my apparatus is as follows: The standards 22 are located on the working bed in accordance with the length of the beam. Cables are threaded with respect to the anchoring and tensioning means, and through the standards 22. Also the cables are threaded through the end plates 21 of the form. The harping units are located between the standards 22 in accordance with the extent and curvature of the desired deflection. The rods 23 of the yokes are engaged with the several strands and the yokes 26 attached to the rods 27 and 27a. The strands of the reinforcement are tensioned a predetermined amount by the means 14. In some instances the amount of tension applied at this point to the various strands may vary to a predetermined degree in accordance with the positioning of the strands in the final beam and the extent of deflection to follow. It may be mentioned at this point that tensioning before deflecion is carried out to such an extent that after deflection the tension is within the limits desired.

Following the operation outlined above, the harping units are caused to pull downwardly upon the cables to secure the desired degree of deflection. This is accomplished by turning the nuts 41 to pull the cables 33 and thus pull the yokes 26 downwardly the desired amount. After deflection to the desired extent, the side walls of the form are applied and the wet concrete mix reintroduced. Vibration and like techniques are applied to properly compact the concrete. After the concrete has hardened, the jacking means is relaxed and the strands at the ends of the beam are severed as by cutting or burning. Release of tension is accompanied by a substantial amount of end-wise contraction of the beam, which is accommodated by the har'ping units because of the cables 33 which provide articulated conuections that accommodate a substantial amount of movement of the members 27, 27a longitudinally of the bed. Cables 33 are maintained tensioned until after releasing the tension of the reinforcing strands, thereby retaining the beam to prevent lateral bowing. Then the tension on these cables is released and the cables are disengaged from the rods 27, 27a by pulling the pins of the sheaves 32, and thereafter rotating the members 27, 27a to disengage them from the yokes 26. The holes left by the members 27, 27a are filled by suitable grouting. Instead of using such rod-like members, less expensive pull rods can be used which can be left in the beam.

It will be evident from the foregoing that I have pro vided apparatus which will permit a predetermined amount of deflection of the reinforcement to obtain the curvature desired. The harping units can be quickly set up for successive casting operations, and readily disengaged after the concrete has hardened and the reinforcing strands released. Because of the ease with which multiple harping units can be applied and operated, it is a simple matter to deflect a plurality of strands to a vertical curvature that closely approximates the theoretical optimum. The harping units are not injured by sudden contraction of the beam when tension on the reinforcement is relieved. In addition to the foregoing the apparatus is relatively flexible with respect to the sizes and types of beams which can be made. Reinforcement can be located in accordance with any desired distribution pattern and all of the strands simultaneously deflected to the extent desired.

The harping means shown in FIGURES 8-10 consists of a frame 46, similar to frame 36, and serving to mount the shaft 47. Two sheaves 48 on shaft 47 are engaged by the pull cable 49. The ends of the cable are attached to a cross head 51 which has threaded engagement with rod 52 and is slidably guided within the frame. A gear 53 is secured to the outer end of rod 52 and is engaged by the pinion 54 on shaft 55. By turning this shaft, as by means of a portable pneumatic motor, the nut 51 and the cable 49 can be moved a desired amount. The looped end of the cable is shown engaging a half sheave 56 or saddle on the lower end of the yoke or fork 57.

In the foregoing I have described my apparatus as being used for casting beams one at a time. For large scale production it is desirable to employ a bed of suflicient length for casting two or more beams simultaneously. In such event the forms are aligned lengthwise, with a space between adjacent ends. Standards 22 are provided between forms and at the remote ends. Each form is provided with end closures 21. The strands are threaded through the forms, the end closures 21 and the standards 22. At one end of the bed the strands are anchored, and at the other end they may be connected to tensioning means. The harping units are applied whereby the desired number of units are provided for each form. After the strands have been tensioned, the harping units are operated to obtain the desired amount of deflection. Casting and release of the strands and harping units proceeds are previously described. The greater longitudinal movement of the beam in this instance, upon releasing the strands, is accommodated by the harping units.

I claim:

1. Apparatus for the manufacture of prestressed concrete beams, comprising a beam casting form, at least one elongate concrete reinforcement member supported within said form, at least one deflecting member located within said form and engaging each reinforcement member intermediate the ends thereof, a frame located adjacent said form, a cross head associated with each deilecting member slidably mounted within said frame, a screw shaft associated with each cross head, each screw shaft being mounted on said frame and being adapted to produce sliding movement of the corresponding cross head, cable means operatively connecting each cross head with the corresponding deflecting member, and roller means journalled within said frame adapted to guide movement of said cable means in a predetermined direction, whereby sliding movement of each cross head will produce bowing in the predetermined direction of each reinforcement member.

2. A device for deflecting a plurality of longitudinally tensioned strands in concrete beam forming apparatus, said device comprising a strand deflecting unit engaged with the strands, means for applying a force to said strand deflecting unit, and means connected between said strand deflecting unit and said force-applying means to transmit applied force to said deflecting unit in a direction substantially perpendicular thereto, said connecting and forcetransmitting means including a rod having a tapered portion with its small end releasably secured to said deflecting unit, and further including an articulated connection between the large end of said rod and said force-applying means, said articulated connection accommodating beam movement occurring when tension on the strands is released, and said rod being releasable from said strand deflecting unit to permit the force-applying means and the connecting and force-transmitting means to be disconnected from said unit.

3. Apparatus for deflecting strands in a prestressed concrete beam form, comprising a strand engaging unit engaged with the strands, a rod having one end connected to said strand engaging unit and the other end projecting through an opening in said form, a saddle, a flexible cable having a bight thereof trained about said saddle, force exerting means connected to the ends of said flexible cable for exerting a pull upon the cable and said saddle, and a pin releasably and pivotally connecting the saddle to the rod exteriorly of the form to enable the cable-engaged saddle to be disconnected from said rod and thereby permit removal of the beam from the form.

4. Apparatus for deflecting strands in an elongated prestressed concrete beam form wherein the ends of the strands are adjacent the ends of the form, comprising a strand engaging unit engaged with the strands between the anchored ends thereof, a rod having one end connected 15 to said strand engaging unit and the other end projecting downwardly through an opening in said form, a saddle, a pivot pin releasably and pivotally connecting the saddle to said other end of said rod, a flexible cable trained around said saddle, and means connected to said flexible cable for exerting a pull thereon and upon the strand engaging unit to deflect the strands within the form to a predetermined extent.

References Cited in the file of this patent UNITED STATES PATENTS 453,482 Jack June 2, 1891 460,213 McCarthy Sept. 29, 1891 736,718 Grimm Aug. 18, 1903 778,416 Kyle Dec. 27, 1904 780,321 Burkholder et a1. Jan. 17, 1905 1,068,442 Mills July 29, 1913 2,016,575 Nemec et al. Oct. 8, 1935 2,278,817 Zeindler Apr. 7, 1942 FOREIGN PATENTS 5,537 Great Britain Apr. 1, 1889 144,193 Great Britain June 10, 1920 

